1. Field of the Invention
This invention relates to devices for effecting outer lead bonding in a tape automated bonding process, and more particularly to such devices which are capable of effecting lead forming simultaneously with the outer lead bonding.
2. Description of the Prior Art
In recent years, the tape automated bonding process utilizing tape carriers is replacing the wire bonding method in an increasing areas of applications as a technique for making electrical connections of the electrodes of semiconductor chips such as integrated circuits or transistors, for the tape automated bonding method has many advantages over the wire bonding method, such as the mass productivity thereof. In this tape automated bonding process, the semiconductor chips are first bonded to the patterns of leads carried by a carrier tape of a flexible material in the inner lead bonding process. In certain areas of applications, the leads and the semiconductor chips thus bonded together in the inner lead bonding process are then bonded to lead frames or substrates of printed circuits in the outer lead bonding process. FIGS. 1 and 2 show such outer lead bonding process effected by conventional devices.
The bonding device of FIG. 1 comprises a bonding stage 1 and a pair of bonding tools 2. The semiconductor chip 6, which has bumps 6a, i.e., projecting electrodes for making electrical connections, is bonded to the inner lead portions 4a of the leads 4 supported by the lead supporting portion 3 of the carrier tape. In the outer lead bonding process, the leads 4 bonded to the semiconductor chip 6 in the previous inner lead bonding process are bonded, for example, to a lead frame 5 by the bonding device. More precisely, the outer lead portions 4b of the leads 4 are bonded to the inner lead portions 5a of the leads of the lead frame 5 having a die pad in a center of each pattern of leads, on which the semiconductor chip 6 is positioned and bonded. The outer lead bonding is effected by lowering the bonding tools 2 to bond the outer lead portions 4b of the leads 4 and the inner lead portions 5a of the lead frame 5 by the thermocompression method.
Before the outer lead bonding as described above, however, the leads 4 must be formed into a step form; the reason therefor is as follows. As the upper surface of the bonding stage 1 is flat, the upper surface of the inner lead portions 5a of the leads of the lead frame 5 are sunk below the portions of the leads carried by the tape carrier 3 by a height G. Due to this level drop G of the upper surface of the inner lead portions 5a of the leads of the lead frame 5 with respect to the portions of the leads 4 near the bumps 6a on the upper surface of the chip 6, it is necessary to form the leads 4 substantially into step forms as shown in the figure before the outer lead bonding process.
In the case of the device of FIG. 2, the bonding stage has a recess 1b so that the above described level drop G is small. Thus, the forming of the leads 4 before the outer lead bonding are not necessary. However, due to the existence of the recess 1b, it becomes necessary to bend the lead frames so that the die pad portions 5b are sunk with respect to the inner lead portions 5a of the leads thereof by a level difference corresponding to the depth of the recess 1b of the stage 1.
Thus, the conventional bonding devices shown in FIGS. 1 and 2 have the following disadvantages. In the case of the device of FIG. 1, lead forming should be performed before the outer lead bonding, especially in the case in which the level drop G is great. Thus, an additional step of lead forming becomes necessary for which expensive dies for forming leads are necessary. In the case of the device of FIG. 2, the additional step of forming the lead frames to bend the lead frames so that the die pad portions 5b are sunk below the inner lead portions 5a of the leads thereof.